FR2474533A1 - HEAT-RESISTANT MECHANICAL PIECE AND PROCESS FOR PREPARING THE SAME - Google Patents

Abstract

THE PART IS MADE OF A CENTRAL PART 2 OF HEAT-RESISTANT MATERIAL AND OF A SURFACE LAYER 1 MADE OF A COMPOSITE MATERIAL WHICH IS SPRAYED THEREIN; THE COMPOSITE MATERIAL IS CONSTITUTED OF ONE PART OF AN ALLOY COMPONENT CONTAINING 1 TO 12 AL, PREFERREDLY 3 TO 8 AL, 10 TO 30 CR, SMALL QUANTITIES OF ONE OR MORE ELEMENTS AS IF , MN, CO, Y AND HF, THE REST IS IRON, AND ON THE OTHER HAND OF A SMALL QUANTITY OF AN OXIDE-TYPE COMPONENT CONTAINING ALO AND POSSIBLY ONE OR MORE OXIDES OF THE OTHER METALS OF COMPONENT D 'THE ALLOY, THE PORES AND THE OXIDE-TYPE COMPONENT FORMING ELONGATED AND NARROW REGIONS WHICH COVER OR PARTIALLY SURROUND THE ALLOY COMPONENT; THE SURFACE COAT IS APPLIED BY JET SPRAYING OR BY ELECTRIC ARC WITH A SMALL CONTROLLED OXIDATION. APPLICATION TO BLADES OR TURBINE FINS.

Description

The present invention relates to a mechanical part

  heat-resistant and a process of its preparation.

  More particularly, the invention relates to a part

  heat-resistant mechanics, such as a turbine blade

  gas nozzle, fin or the like, for use in a hot gaseous environment, particularly in a

  dynamic mechanical stress, and a process for its preparation

  tion. The parts of the gas turbines are subjected, in use, to extremely high stresses due to

  the mechanical forces caused by the gas pressures

  its elevated and rotational speeds and other hand to

  high temperatures that vary rapidly. The desire to obtain

  yield ever greater, requires that the materials

  used are resistant to such constraints and in particular

  at high temperatures, corrosion and erosion.

  The high temperature mechanical resistance of the materials

  steel, nickel or cobalt, is greatly reduced to 850-9000C. Basically, these materials can not be used at higher temperatures

  and it is impossible to improve them.

  Another attempt has therefore been made to obtain a useful material at higher temperatures. Examples of such materials are cermets, which are highly refractory materials based on metal and ceramic whose ceramic phase consists essentially of carbides or refractory oxides. Also some molybdenum alloys

  maintain high mechanical strength up to 1200 ° C.

  However, by nature, cermets are fragile and allergy

  molybdenum treatments are not sufficiently resistant to oxidation

  and can not be improved by alloying techniques.

  To solve the problem of obtaining a material

  having the desired properties, a process is known which

  it is possible to apply a protective layer to the surface, this application can be carried out in various ways, for example by mechanical plating, diffusion, chemical plating,

  electrolytic deposition, quenching, spraying and enameling.

  To protect the gas turbines against high temperatures, it has been proposed to form high temperature resistant coatings by spraying, for example zirconium oxide. According to the article "ZrO2 coatings on NIMONIC alloys", by J.M. Nijpjes in High Temperature Materials, 6 Plansee Seminar, 1968, p. 481, the objective is to raise the operating temperature of an industrial gas turbine from about 2000C to about 400C to increase the power of this turbine. The basic material used is NIMONIC 115 (trademark of an alloy containing 18%

  of chromium, 5.2% of molybdenum, 2.3% of titanium, 0.8% of aluminum

  nium, 38% nickel, the rest being iron) which is one of the

  the strongest nickel-based materials we know

  is. The maximum temperature possible with this alloy is 1 0000C and therefore it must be protected when the

  temperature is higher. For this purpose, we apply

  first, by plasma and then by jet, a layer of oxy-

  thick zirconium of about 1 mm. In this case the poro-

  The size of the jet spray layer is significantly higher than that of the plasma sprayed layer. The author indicates that a 1 mm thick zirconium coating makes it possible to produce gas turbines operating with an inlet temperature of between 1 2000C and 1 4000C, but problems due to the surface roughness and the porosity of the layer of

oxide arise.

  In the same reference, page 803, "Corrosion resistant coating for refractory metals and super-alloys", J. D. Gadd indicates inter alia the vacuum crate diffusion of an aluminide in nickel-based alloys. During this

  operation it essentially forms a phase f of NiAl.

  Another method for coating a turbine blade is vacuum coating and this process is also described in the aforementioned reference 854 by A. M. Shroff under the title "Vapor deposition of refractory metals". The layers applied according to this process are very thin but on the other hand they have a high density of 98.5 to 99% of the density

  theoretical and can be made gastight.

  Vacuum coating formation of superimposed

  thin software is also described in the publication of

  Swedish patent No 345 146 of 15 May 1972. In this case the

  surface area consists of 20 to 50% chromium, 10 to% aluminum, 0.03 to 2% yttrium (or one or more

  rare earth metals), the rest being iron. The thick-

  the layer is very small (about 0.07 mm) and

  therefore the surface layer can not always ensure

  to provide sufficient thermal shock resistance to the

  canic coated. In addition, the aluminum of the surface layer

  tends to diffuse into the base material, so that the protective oxide coating disappears. So that the service life is acceptable, the percentage of aluminum must be at least 10% by weight and preferably have a value

higher than 12 to 14%.

  In contrast, the invention relates to the application of a

  protective layer by thermal spraying. We have previously

  proposed to spray a layer having the composition Ni-Cr-B, NiSi-B or Al-Si-Cr. These protective layers are of course ductile and they are resistant to mechanical shock

  but they have a low resistance to thermal cycling.

  The layers also have low erosion resistance but they can withstand oxidation up to at least

1000-1000C.

  Published Patent Application No. 2,842,848 in the United States

  Federal Republic of Germany suggests further to increase the resistance

  oxidation of superalloys, to spray a coating

  wherein the composition is M-Cr-Al-Y, wherein M is a member selected from nickel, cobalt and iron and which preferably contains 10 to 40% chromium, 8 to 30% aluminum, 0.01 Yttrium% and 5 to 85% chromium carbide particles are dispersed. A spray applied coating

  plasma has withstood 500 hours at 9270C without any cracking

  ration. U.S. Patent No. 4,145,481 discloses

  written a suitable coating for example for gas turbines which is obtained by hot isostatic pressing. In this case also, plasma spraying is applied

  layer having the composition Co-Cr-Al-Y.

  The object of the invention is to obtain a super-layer

  suitable for mechanical parts and a method for

  manufacture such parts so as to ensure a good resistance

  at high temperatures, even in the case of

  temperature, good resistance to oxidation,

  erosion even in the presence of highly corrosive gases and excellent mechanical resistance in the presence of

  static or dynamic, in particular

  your. The mechanical part of the invention consists of a central part made of a material resistant to heat and

  a superficial layer sprayed on this central part

  and consisting essentially of a Fe-Cr-Al alloy, the

  characteristic of the invention being that the superficial layer

  is composed of a composite material the nature of which is

  defined in the characteristic part of claim 1.

  Other relevant features are contained in the

2 to 6.

  In addition, as shown in claims 7 to 10,

  preferably, the mechanical part of the invention is prepared by jet or electric arc spraying of an alloy of

  particular composition preferably in the form of a yarn.

  The corrosion resistance can be further increased by subsequent mechanical treatment of the surface layer by

example by molding or polishing.

  The composite material forming the surface layer

  consists of an alloy component and a small quantity

  one-component oxide type. The alloy component

  contains (by weight) 1 to 12% aluminum and preferably 3 to 8% aluminum, 10 to 30% chromium, small amounts of one or more elements selected from silicon, manganese,

  cobalt, yttrium and hafnium, the rest being iron, tan

  say that the oxide component contains aluminum oxide

  minium (A1203) and optionally one or more oxides of

  other metals of the alloying component.

  The oxide content of the surface layer should not exceed about 5% by volume and the porosity of the layer

  shall not exceed 8% and preferably 1 to 4%.

  The structure of the surface layer appears in the attached single figure which is a photomicrograph showing a composite layer 1 sprayed on a central portion 2 made of a Fe-Cr-Ni alloy (magnification about 120 times). The pores and the oxide-like component in the layer

  surface areas form elongated and undulating

  (corresponding to the black lines of the figure)

  essentially parallel to the interface (or

  face of the diaper), so as to overlap or partially enclose

  the alloy component. The thickness of the regions is at most 2 μm and is normally about 0.1 to 0.5 μm.

  To date, attempts have been made to produce superficial layers

  very thin shafts when coating turbine blades

  with Fe-Cr-Al type alloys, for example by means of

  vacuum garment. However according to the invention it is suggested to

  spray the protective superficial layer over a thick layer

  it is relatively large, ie at least 0.15 mm, in particular from 0.3 to 3.0 mm (residual thickness after a possible mechanical treatment). This produces a screen

  because the surface layer has a thermal conductivity

  lower than that of the heat-resistant alloy which normally constitutes the central part and which is

  example a steel-chromium (13% chromium), a steel nickel-

  chromium (18% chromium, 8% nickel), one of the alloys known under the following trade names: NIMONIC 75, HASTELLOY X, INCONEL 600, INCOLOY 800 and similar materials. The heat shield protects the central part against excessive temperatures and especially against thermal shocks. The heat shield dampens sudden changes in temperature which helps to prevent cracking caused by

  thermal shocks. The heat shield is particularly effective

  because the thermal conductivity of the surface layer

  is weaker transversely to the surface than parallel-

  as a result of the undulating structure of the

  superficial composite that makes it anisotropic (see microphotography). A rather thick surface layer according to the invention also has a good vibration absorption capacity and by

  therefore the dynamic mechanical strength is still

  liorée. The soundproofing effect is also very good.

  The spraying operation is carried out according to a

  known per se for example with a spraying apparatus

  jet or electric arc spraying, as

  previously described in Swedish Patent No. 7807523-1.

  According to the invention, a wire having the aforementioned composition of the alloying component is preferably used. We perform

  the spraying operation with low oxidation

  controlled by using for example argon as atomic gas.

  tion. The composite material and the aforementioned regions which

  partially rotate the alloy grains form spontaneously

  ously. The diameter of the wire is from 1.5 to 5 mm and preferably from 2.0 to 2.5 mm and the particular value is chosen according to

  the desired thickness of the layer.

  If the mechanical part must be exposed to temperatures

  very high levels, it should be mechanically

  the surface layer formed by spraying to obtain

  keep a surface as smooth as possible. We can perform

  this treatment by grinding or polishing and the thickness eli-

  It is normally about 0.2 to 0.3 mm thick. As before

  indicated, the residual thickness of the layer must be

  at least 0.15 mm. As a result of the improved super polish

  fective, corresponding to a maximum roughness RA5, one obtains a very good resistance to corrosion and erosion. The

  hardness of the layer is about 230 HB.

  To obtain sufficient adhesion between the central part and the surface layer, it is necessary in certain cases to spray first on the central part a very thin union layer, for example nickel-aluminum

  or copper, and then apply only the outer layer

  composite sky. This type of union layer or inner layer

  The intermediate is also used to prevent diffusion, for example nitrogen and aluminum, between the surface layer and

  the central part. In the case where the difference in the coefficients

  thermal expansion between the central part and the composite surface layer is relatively important, it may also be appropriate to apply at least one layer

  intermediary to obtain a good transition between

  underlying material and the coating material. In the example

  illustrated, the coefficients of thermal expansion of the

  The central and superficial layers have approximately the same importance, ie 19 x 10 6C and 14 x 10 8gC respectively.

  and for this reason an intermediate layer is not needed.

  necessary. The coated elements according to the invention have been found to resist corrosion in an oxidizing atmosphere at temperatures up to about 1350 ° C. In addition to gas turbine blades, the coating can be used in a variety of applications. Practical tests yielded results

  satisfactory in the case of coverings of chambers of com-

  combustion of internal combustion engines, protective layers

  on molybdenum electrodes and

  protection against corrosion of fan blades in furnaces. The material in the boiler of a steam plant was also studied by exposing the surface layer at a temperature of about 800 to 9000C for 7000 hours in an atmosphere containing 1000 ppm of SO2. The depth

  surface corrosion was only 50 pim.

  As a substrate of the superficial layer, it is possible to use

  a variety of metallic materials, for example mild steel,

  molybdenum, chrome steel, chromium steel,

  nickel as well as the materials marketed under the following names: KANTHAL, NIKROTHAL, SUPER KANTHAL, INCOLOY, HASTELLOY, INVAR, NIMONIC, INCONEL, etc.

Claims (10)

  1. Heat resistant mechanical part, for example blade or gas turbine blade or the like, intended for   be used in a hot gaseous environment, in particular   to bind with a dynamic mechanical stress, consisting of a central part made of a material resistant to heat,   possibly at least one intermediate layer and one   spray-applied surface layer consisting essentially of a Fe-Cr-Al alloy, characterized in that   the surface layer consists of a composite material   having a porosity of not more than 8% by volume and consisting of   a part of an alloy component containing 1 to 12% aluminum   nium, preferably 3 to 8% of aluminum, 10 to 30% of chromium, small amounts of one or more of the group consisting of silicon, manganese, cobalt, yttrium and hafnium, the remainder being iron, and on the other hand a small amount of an oxide-type component containing aluminum oxide (Al 2 O 3) and optionally also one or more oxides of the other metals of the alloy component, the   pores and the oxide-like component forming regions.   narrow or narrowly covering or surrounding the alloy.   2. Mechanical part according to claim 1, characterized   in that the regions are undulating and have a primary direction   almost parallel to the surface of the superimposed ficial.   3. Mechanical component according to one of claims 1 or 2,   characterized in that the oxide content of the superimposed   is not more than 5% by volume.   4. Mechanical part according to any one of revendica-.   tions, characterized in that the porosity of the   superficial layer is 1 to 4% by volume.   5. Mechanical part according to any one of the claims   the thickness of the surface layer is at least 0.15 mm. = 6. Mechanical part according to claim 5, characterized in that the thickness of the surface layer is included between 0.3 and 3.0 mm.   7. Process for preparing a mechanical part, in particular   bonding a blade or blade of a gas turbine or the like, for use in a hot gaseous environment, in particular with dynamic mechanical stress, wherein the mechanical part is produced by spraying a surface layer consisting mainly of a Fe-Cr-Al alloy on a central part made of a material   resistant to heat, possibly with at least one   medium, characterized in that the pulverulent   of the surface layer by spraying or arc-spraying an alloy of 1 to 12% aluminum, preferably 3 to 8% aluminum, 30% chromium, small amounts of one or more members of the group consisting of silicon, manganese,   cobalt, yttrium and hafnium, the rest being iron, this   the spray operation being carried out with a small   controlled oxidation to form a surface layer   carrying not more than 8% by volume of pores and containing firstly an alloying component having said composition and other   a small amount of a constituent oxide component   aluminum oxide (A1203) and possibly one or more   oxides of other metals of the alloying   what the pores and the oxide component form   elongated and narrow limbs covering or surrounding the alloy component.   8. Process according to claim 7, characterized in that   that the alloy is brought in the form of a wire.   9. Method according to claim 8, characterized in that the wire diameter is 1 to 5 mm, in particular 2.0 at 2.5 mm.   10. Process according to any one of claims 7   at 9, characterized in that after the spraying operation the surface of the surface layer is subjected to a finishing to increase polish.